


Into the Deep End

by idontevenknowugh



Series: Black and Blue [2]
Category: Undertale (Video Game)
Genre: BDSM, Bondage, Fire play, Impact Play, Multi, No Smut, Safeword Use, Sanscest - Freeform, bloodberry, flogger, swapfellcest - Freeform
Language: English
Status: Completed
Published: 2017-03-14
Updated: 2017-03-14
Packaged: 2018-10-05 01:26:15
Rating: Explicit
Warnings: Graphic Depictions Of Violence
Chapters: 1
Words: 2,025
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/10294265
Author URL: https://archiveofourown.org/users/idontevenknowugh/pseuds/idontevenknowugh
Summary: “There’s a few new rules to what we’re going to do today.”Black continues Blue’s education, kind of.





	

**Author's Note:**

> A birthday gift for sinssansguilt! I have had such a great time chatting with you these past few months, and I hope that you have a fantastic day! 
> 
> I also hope you like this continuation of BaBaRaO (what an acronym!) despite it being pretty smutless. It’s kind of a transition chapter, so I apologize for that, but I hope you will also take as your gift my intent to continue this as a series of fics about Blue learning from Black ,with a rotating cast of subs via Slim, Red, and, eventually, Stretch. I would have never found the inspiration to continue it if I hadn’t started this fic for you, based on your desire to see more Swapfell and more Black and Blue together. I hope I can create something you’ll really enjoy.

Black had a problem. His boot tapped an anxious rhythm against the leg of his chair as he mulled it over. Glancing up, he realized that Slim wasn't eating. The tall skeleton was watching him with a patient expression. Realizing he was letting his irritation show, Black gave Slim a sharp look and stabbed his fork into the cooling plate of enchiladas in front of him.

Slim flinched at the sharp clack of metal hitting the plate and looked down at his own, sadness making his features droop. Black sighed and let his fork fall with a clatter. Slim looked up at him as Black stood and made his way around the table.

He stopped behind Slim and stroked his skull fondly, pulling it back against his rib cage. He could feel more than hear Slim hum in pleasure at the contact.

“I’M NOT UPSET WITH YOU, BROTHER. I HAVE A MATTER WHICH I FIND MYSELF TORN ON, THAT IS ALl.”

“Is it,” Slim turned slightly to nuzzle into Sans’s hand, “something I could help with, my lord?”

Black looked down at his brother thoughtfully. Could Slim help? He had excluded his brother before, but he had made some assumptions at that time which proved to be wrong. Of course, knowing that didn't exactly fill him with confidence at making this next, tough decision.

“PERHAPS, BROTHER,” he responded thoughtfully. Including Slim still worried him, but when he put that aside, was there really another choice? Blue’s inexperience was risky enough. Slim knew what he was doing and trusted Black implicitly.

“PERHAPS.”  
——-  
“There are a few new rules to what we’re going to do today.”

Blue nodded, his eyelights flickering between Black and Slim. Black smirked, fully aware that his brother made for a distracting sight. He hadn’t been able to resist some extra touching while he got Slim into the setup, himself.

“First, more intense play requires more than a safe word. If Slim particularly likes what we’re doing when experimenting, or if we check with him and he is fine, he will say,” Sans paused and pointed at the tall monster without looking.

“Green,” was said softly behind him.

“Or one tap if he’s gagged. He will never, ever be bound in such a way that he does not have one of those modes of communication at his disposal. Understood?” Black asked, voice deadly serious.

Blue nodded, watching only Black now. There was a slight flush to his cheeks, but Black wasn’t sorry for sounding harsh. He would put his brother’s safety above anyone’s pride, even his own. He’d learned that lesson well enough.

“Yellow means he’s uncertain or uncomfortable with what we’re doing. We don’t need to stop the scene, but we may need to loosen a tie or change our play. Two taps, if he’s unable to speak. Red, or three taps, means full stop and we untie him immediately.” Black met Blue’s eyelights. “These are for your use as well. We won’t know what you like until we try things. If you don’t like them, tell me.”

“Okay.” Blue replied. The reminder that they were trying something new led his eyelights to wander of the assembled tools. Black hoped his intent wasn’t too obvious yet. If it was, Blue didn’t say anything.

“Then let’s get started.” Black smirked and turned to face Slim, who, other than his assistance in the explanation, was watching them silently. He was naked and bound, but wasn’t gagged. Per Black’s own rules, he couldn’t be. The way his arms were tied, laying over the back of the chair, they were dangling away from the wood and each other. He couldn’t easily produce the taps.

His legs were also tied, to the legs of the chair. Sans had enjoyed making the complicated series of knots, which wound between his brother’s tibiae, fibulae, and the chair itself with an almost braided look. It left Slim quite unable to move.

“Let’s start you off with one of the more versatile tools I have,” Black picked up his flogger off the table as he said it. When he offered it to Blue, he got a wide eyed stare for a few moments before Blue gingerly took it from him. He looked it over with a reverence that Black appreciated.

“You can hit him with it, obviously, but he also enjoys having the strands run along his bones.” That drew a needy sound from Slim.

“Beyond that, it’s up to you to find his limit.” Black tried to make the statement sound as casual as all the rest. Blue did not need Black’s anxiety on top of his own nervousness. The best way to make their sessions safe was to have Blue confident as well as cautious. Nerves made mistakes.

Phalanges clenched into fists, Black stepped away to observe. Blue, as expected, immediately went with Black’s suggestion of drawing the soft leather across Slim gently. While Blue had insisted, when he came to Black asking for further education, that he had enjoyed everything, Black was skeptical. His softer counterpart had been alarmed at the paddle. If he couldn’t even bring himself to do this, then there wasn’t much point in going further.

After a few minutes of the same, Blue flopped the flogger against Slim’s ribcage with no impact whatsoever. Black grit his teeth, resisting the urge to step in and instruct Blue. He knew how well he would take such a lecture. However, after a few such sad attempts, Blue turned to him, face bright.

“I don’t know if I can…” He said sadly. Black winced. Maybe the hands off approach was the wrong one for Blue. As similar as they were, they had their differences.

“Try standing to the side,” Black stepped forward and gently led Blue to Slim’s left until he was lined up for a straight downward strike with the flogger, “and striking across his femur. It’s easier to hit and a nice sturdy bone.”

Instead of returning to his spot, Black stood just far enough away that he wouldn’t be in Blue’s way, at an angle he could see Slim’s face. He was giving Black a small smile and seemed relieved. Black had warned Slim this wouldn’t be a normal session, but he had insisted on helping.

As Black watched him, there was a soft smack and Slim’s smile twitched up higher. Turning back to Blue, he watched him raise his hand and essentially let it fall down, the flogger hitting with little more than gravity behind it. When he noticed Black watching, Blue turned to him with a questioning look. Black nodded, and Blue raised his hand again.

His hits grew harder, but very gradually, and Black relaxed some. Slim would have plenty of time to warn him if he got close to his threshold. That was a pretty big if at the rate Blue was going, however. For now Slim was fidgeting with barely restrained need. The light hits were just teases of what he really wanted.

Finally, after Black had pointed Blue to the other side to even out the sensation, Blue hit Slim hard enough to draw out a hiss of pleasure. Blue stopped with a squeak, the sound startling him. He held the flogger up to his sternum, gripping it with both hands nervously. Slim turned to look him in the sockets.

“Green,” he said with a husky intensity that sent shivers down Black’s spine. Blue reacted immediately, eyelights growing and shoulders losing their tension. He drew back and this time there was a good solid crack from the hit, Slim’s skull dropping back with a groan. Blue looked over at Black, as if looking for confirmation that it was okay.

“Listen to your sub first and foremost.” Black offered as advice. “Unless they suggest something truly idiotic,” he added wryly, making Slim chuckle. Blue nodded and struck Slim’s femur firmly a few more times. Slim reacted similarly, gasping and groaning. The sounds went straight to Black’s pelvis, and he was soon holding back his need so that they could move forward. Thankfully he was well practiced at that. His play with his brother often included a contest to see who would give in to arousal first. He rarely lost.

“Would you like to move on?” Black asked Blue, ignoring his brother’s whine of disappointment. Blue nodded eagerly and handed the flogger back to him, near bouncing with excitement. Well, that was a good sign. “Allow me get a few things…”

Black winced a little as he turned to the table with his supplies on it. Was that…regret? He didn’t really relish the idea of putting Blue through this, in the end. They were good friends and, though he would be loathe to admit it, Black had grown fond of the other monster. The idea of training him was appealing far beyond what he had expected. Sentiment, however, was no reason to sacrifice safety.

“Now, pay attention,” he said with mock calm, turning back to face the other two. One set of phalanges held a candle, the other a lighter. Blue’s eyelights shrunk at the sight. He opened his mouth, but Black talked over him.

“Fire play is not for the feint of soul, but then, we aren’t, are we?” Black smirked, swallowing anxiously, and lit the candle before holding it out to Blue. The other monster stared at it, his mouth opening once and then closing. He reached out and took it, though Black noticed he was trembling. The flame flickered as Blue pulled it back.

“Go on.” Black prodded when Blue stood unmoving for several minutes. Slim was watching the flame with an ambiguous look. Not scared, but not excited like he’d been with the flogger.

Blue walked forward a few steps and then turned to Black with a worried expression.

“I don’t think I’m ready for this,” he said, and looked away, flushing with shame. Black grit his teeth and stepped up to gently turn Blue back towards Slim.

“Nonsense. You have all the tools you need.” Black said, waving his hand with a showmanship that was entirely unnecessary. It wasn’t even a lie. Blue’s attention to his sub, cautious manner, and knowledge so far would likely get him and Slim safely through just about any kind of play. There was just one thing that Black felt he needed to see before he could comfortably teach Blue everything he knew.

“Still, it seems like…” Blue trailed off, voice thick. A sharp pang of guilt hit Black, unfamiliar and unwelcome, at the realization Blue might think he would refuse to teach him if he didn’t continue. That was not at all what he intended, and made the stakes far more heavy on the side of stopping than they were in play. Before he could say anything to alter that perception, Blue spoke up again.

“Red,” he said, soft but firm. Black relaxed, bones appearing around Slim to cut him free while he reached forward, enveloping Blue in a hug and putting out the candle with two digits.

“My lord!” Slim cried, rushing forward, but Black waved him off. Blue had turned to look at him with shrunken eyelights and tears running down his cheekbones. Black frowned, sad to see his friend in such a state.

“My apologies. You aren’t ready, if only mentally, but I had to push you.” Black squeezed Blue, and then released him. Blue stepped away, looking at him for further explanation.

“I wanted to see you set a hard limit, even with me pressuring you.” He offered. “I know I can be…enthusiastic,” Blue smiled a little at that, “but I never want you to let me override your comfort or concerns. Understood?”

Blue nodded, his smile growing, but still soft. His tears slowed to a trickle, and then stopped. When he took a half step towards Black, it was for an easy embrace. Relief washed through Black. It wasn’t often that Blue didn’t use his words, but Black knew that those moments were the most meaningful. Hugging Blue back, he didn’t feel any wetness around his sockets at all. That would be ridiculous. 

**Author's Note:**

> My tumblr is where I: take requests, post streams, chit chat, do teasers, try out new fics, reblog a lot of skeleton porn, pimp all my favorite fics


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